Obesity is the leading cause of chronic illness and premature death in the United States. The goal of this proposal is to further our understanding of how obesity develops and how obesity causes metabolic disease. In particular we will investigate an area that we developed during the last funding cycle - the regulation of adipocyte mitochondrial biogenesis and metabolism by Wnt signaling. Exposure of cultured adipocytes to Wnt3a activates signaling pathways and increases expression of mitochondrial regulators, such as peroxisome proliferator-activated receptor-? coactivator 1? (Pgc1?), mitochondrial transcription factor A (Tfam) and nuclear respiratory factors (Nrfs). In addition, Wnt3a regulates lysine acetylation of a subset of mitochondrial proteins including citrate synthase, whose activity increases with Wnt treatment. Based on these data, we propose experiments to test the hypotheses that regulation of posttranslational modifications on mitochondrial proteins mediates effects of Wnt3a on oxidative metabolism, and that it is Wnt11 that initiates endogenous Wnt signaling in this context. We have found that inhibition of Wnt signaling by secreted frizzled-related protein 5 (SFRP5), which is induced in adipose tissue with obesity, is required for adipocytes to hypertrophy in response to an obesigenic diet, and we propose to use our novel animal models to extend the roles of SFRP5 and Wnt signaling in adipose tissue biology. To test these hypotheses we propose the following specific aims: 1) to investigate mechanisms by which expression of SFRP5 in adipocytes regulates adipocyte hypertrophy and the development of obesity, and 2) to determine mechanisms by which Wnt signaling stimulates mitochondria biogenesis and metabolism. These studies will greatly advance our understanding of the mechanisms that control adipocyte metabolism. Importantly this work will resolve for the field the conflicting data on the regulation and functional roles of Sfrp5 in adipose tissue and glucose homeostasis/insulin sensitivity. Our results will also further our mechanistic understanding of how Wnt signaling regulates oxidative metabolism through acetylation and activity of mitochondrial proteins in adipocytes and with obesity. These findings may also shed light on similar regulatory processes of Wnt signaling on mitochondrial function in liver and muscle. Thus, insights gained from the successful completion of proposed studies will be crucial for our understanding of adipose tissue physiology and the development of obesity and associated metabolic complications.